When a major undersea earthquake or an on-land earthquake occurs near the coast and at a shallow depth, there is a possibility that a destructive tsunami can be generated that will impact near-by coasts within minutes (local tsunami) and that can also traverse across entire ocean basins to wreak havoc 1000’s of miles away and up to 24 hours later (regional or distant tsunami). There are two main ways in which the public can be warned about an on-coming tsunami:
Natural Tsunami Warning Signs:
Natural warning signs can be evident in the case of local tsunamis, where the source of the earthquake is 100km or less from the shoreline which is being affected. Key natural tsunami warning signs which have been highlighted by survivors are:
- Severe shaking of the ground
- The sea pulling back a significant distance exposing reefs, fish and marine life not normally seen
- Unusual roaring sound of the ocean (similar to that of a train)
If you are at the beach and recognize any of the tsunami natural warning signs move immediately to higher ground.
Sometimes tsunamis may occur without the initial pulling back of the sea. In this case, a massive wall of water may be seen approaching land. If you can see the wave you are already too close to outrun it so in these cases, you should go to an upper floor (at least the 3rd storey) or roof of a concrete and reinforced building. As a last resort, climb a strong tree if trapped on low ground. If swept up by a tsunami, look for something to use as a raft.
Do not wait for an official warning bulletin before evacuating as authorities may not have enough time to issue official tsunami warning information. Once in a safe place, you must follow the guidance of the local disaster management officials.
Official Tsunami Warning Information and Bulletins:
To alert far-away coasts, internationally-coordinated tsunami early warning systems have been established to provide alerts to countries on regional and distant tsunamis in particular. For local tsunamis, national authorities may not have enough time to issue official tsunami warning information to the general public, and therefore, it is very important that the public is aware of the natural warning signs and the appropriate actions to take in the event that any of the signs are recognised.
Tsunami Type Typical Time to Impact Tsunami Service Provider (TSP) Response Time
Local : 0-1 hour 2-5 mins
Regional : 1-2 hour(s), 5-10 mins
Distant >2 hour : 10-20 mins
The mission of a TSP or tsunami warning centre (TWC) is to provide early tsunami warning information on potentially destructive tsunamis. International and regional TSPs provide this information to local emergency officials who then provide the relevant information to the public based on established protocols and standard operating procedures (SOPs). In the case of national TSPs, this information may be provided directly to the public, dependent on the relevant protocols and SOPs. TSPs seek to respond fast and with accuracy in order to be reliable and effective.
The current TSPs for the ICG CARIBE EWS are the US National Tsunami Warning Center (US NTWC) and the Pacific Tsunami Warning Center (PTWC). US NTWC covers Puerto Rico, the British Virgin Islands and the US Virgin Islands whilst PTWC covers the rest of the Member States within the Caribbean and adjacent regions. As of March 1, 2016 PTWC started to issue the New Enhanced Products exclusively. These products are based on the recognition that it is the sovereign responsibility of the countries to issue their own alerts and therefore, PTWC will very quickly after an earthquake, dictate whether or not there is a threat and some minutes later how significant it may be. This tsunami threat information has to be interpreted rapidly by the corresponding institutions which then have the authority for receiving and issuing the tsunami bulletins to the local population based on their national alert/threat level system e.g. Warning, Advisory, Watch, etc.
Emergency authorities, such as the National Disaster Management Office (NDMO), civil defence, or emergency operations centres, have the responsibility for immediately interpreting the science-based alerts issued by the TSP (international, regional, national, and/or local), and quickly disseminating safety information to the public on what to do. They are also responsible for informing the public when it is safe for them to return to the evacuated coastlines; due to structural damage, debris, and other life safety concerns, the ‘all-clear’ to return may not be issued by the local authority for hours or even weeks after the event. The NDMO, Civil Defence and or another coastal management agency may also have the ongoing responsibility for educating the public concerning the dangers of tsunamis and for developing safety measures to be taken to avoid the loss of life and reduce property damage.
In the event of a regional and distant tsunamis in particular, it is therefore crucial for the public to monitor the bulletins provided by the local disaster management officials to confirm if a tsunami threat is likely. During any tsunami, the public must follow the guidance provided by the local disaster management officials.
Currently, it is there are difficulties for TSPs to detect landslide and volcanic sourced tsunamis and also to provide early warning information in the case of local tsunamis; except in a few areas.